1. Field of the Invention
The present invention relates to an alignment correcting method for making a position alignment of patterns relative to each other in a horizontal direction when a plurality of patterns are formed in manufacturing a semiconductor device.
2. Description of the Background Art
Alignment will be discussed with reference to the conceptual view of FIG. 52. A semiconductor device comprises a plane 3a having patterns 1a and alignment marks 2a to 2d, and a plane 3b having patterns 1b and alignment marks 2e to 2h. The patterns 1a and 1b are formed on a wafer and made of a silicon compound, metal or the like. The alignment marks 2a to 2d are formed at the same time as the patterns 1a. The alignment marks 2e to 2h are formed at the same time as the patterns 1b. The term xe2x80x9calignmentxe2x80x9d is meant to define the operation of relatively aligning the position of the patterns 1a in the plane 3a for use in the next step with the position of the existing patterns 1b in the plane 3b, for example.
In a process for manufacturing a semiconductor device, several major steps are performed to manufacture the semiconductor device. The major step termed herein means a group of steps for forming one pattern (e.g., a film-formation step for forming a film on a wafer, a resist coating step for coating with a resist, an exposure step, a development step, and an etching step for patterning a film).
FIG. 53 is a conceptual sectional view of a semiconductor device. The semiconductor device of FIG. 53 is provided by performing seven major steps. Since one pattern is formed in each major step, the semiconductor device comprises seven patterns 301 to 307 formed finally in a stacked relation through seven major steps, respectively.
One of the steps which require alignment in one major step is an exposure step. In the exposure step, alignment is performed in practice to relatively align the positions of a reticle and a wafer with each other. Apparatuses for exposure and alignment include, for example, a step-type projection aligner (referred to hereinafter as a xe2x80x9cstepperxe2x80x9d).
FIG. 54 is a block diagram of a production system 10 for manufacturing a semiconductor device. The production system 10 comprises a production control system body 6 for controlling the manufacture of a semiconductor device and connected to a stepper 4 as mentioned above, an overlay checking device 5, and other semiconductor manufacturing devices 7 through reference terminals 8. The production control system body 6 may be connected to a plurality of steppers 4 and to a plurality of semiconductor manufacturing devices 7 such as a sputtering device and an etching device.
The production system 10 uses the semiconductor manufacturing devices 7 including the steppers 4 to form, for example, a plurality of semiconductor integrated circuits 21 on a wafer 20. Lead frames, leads and packages are added to the semiconductor integrated circuits 21 in an assembly step for formation of semiconductor devices. The above-mentioned planes 3a and 3b of the semiconductor device correspond to, for example, layers of the semiconductor integrated circuits 21.
The stepper 4 connected to the production control system body 6 has an alignment function for exposing the same wafer to a plurality of shots of light. Unfortunately, there arises a shear between the patterns aligned by the stepper 4 despite of the alignment. The shear is due to various causes such as a mechanical error of the stepper itself and a reticle manufacturing error. The stepper 4 is given a correction value for eliminating the shear (referred to hereinafter as a xe2x80x9cstepper correction valuexe2x80x9d). On the other hand, the overlay checking device 5 detects the shear to calculate a correction value for eliminating the shear (referred to hereinafter as an xe2x80x9coverlay checking correction valuexe2x80x9d). The detection of the shear in the overlay checking device 5 is termed xe2x80x9coverlay checking.xe2x80x9d
The production control system body 6 controls data on alignment (referred to hereinafter as xe2x80x9calignment dataxe2x80x9d) which are provided from the stepper 4 and the overlay checking device 5. The alignment data include the overlay checking correction value, the stepper correction value, the type of a wafer (lot No., product No. and the like), the date and time when alignment was performed, the contents of processing, a production history and the like. The alignment data are stored in a database 6b. 
An alignment correction unit 6a is one of the functions of the production control system body 6, and calculates the stepper correction value, for example, using the alignment data stored in the database 6b. 
The stepper correction value calculated includes a stepper correction value for a wafer component, and a stepper correction value for a shot component. The stepper correction value is applied to the stepper 4. FIG. 55 conceptually illustrates a structure of the stepper 4. The wafer 20 to be exposed is placed on a wafer stage WST. A reticle 30 formed with a pattern image to be drawn on the wafer 20 is provided on a reticle stage RST. An illumination system ILS directs a light beam for exposure onto the reticle 20 on the reticle stage RST. The light beam for exposure passed through the reticle 30 is refracted by a lens system PL to form an image 34 on the wafer 20. The stepper 4 is adapted to move the wafer stage WST in accordance with a value set by the stepper correction value for the wafer component to move the wafer 20 on the wafer stage WST. The stepper correction value for the wafer component includes information about offsets X and Y (base line), scalings X and Y, X-Y orthogonality, wafer rotation and the like. The stepper 4 is also adapted to change the image 34 directed from the illumination system ILS through the reticle 30 and the lens system PL onto the wafer 20 in accordance with the stepper correction value for the shot component. The stepper correction value for the shot component includes information about shot rotation, magnification and the like. As the reticle stage RST rotates about a central axis 32 in accordance with the setting of the shot rotation, the image 34 is rotated. The degree of magnification of the image 34 is changed depending on the difference in the degree to which the lens system PL and the like refract the light beam for exposure in accordance with the setting of the magnification.
The wafer processing controlled by the production control system body 6 will be discussed below. The alignment of the pattern 304 of FIG. 53 will be taken as an example. The control of the production control system body 6 is performed according to the flowchart of FIG. 56. First, the production control system body 6 transports a wafer 20 to be processed to the stepper 4. When the wafer 20 to be processed reaches the stepper 4, the alignment correction unit 6a calculates the stepper correction value (Step S901 of FIG. 56). The production control system body 6 sets the stepper correction value obtained by calculation for the stepper 4 reached by the wafer 20 to be processed (Step S902). The stepper 4 performs alignment (Step S903). After the completion of the alignment, the production control system body 6 registers the stepper correction value for the wafer to be processed in the database 6b to control the stepper correction value. After the processing in the stepper 4, the production control system body 6 transports the wafer 20 from the stepper 4 to the overlay checking device 5 (Step S904). The overlay checking device 5 detects a shear between the pattern 304 and the pattern 303 immediately therebelow with the positions of the alignment marks (Step S905). Further, the device 5 calculates the overlay checking correction value for elimination of the detected shear (Step S906). Subsequently, the production control system body 6 collects overlay checking correction values from the overlay checking device 5 (Step S907). The system body 6 stores the collected overlay checking correction values in the database 6b to control them (Step S908). The production control system body 6 transports the wafer 20 to be processed to the semiconductor manufacturing device 7, as needed, where sputtering, etching and the like are performed.
Next, a conventional alignment correcting method for calculating the stepper correction value will be discussed with reference to FIGS. 57 and 58. It is assumed that the stepper correction value set in Step S902 is +1 and the overlay checking correction value (which herein corresponds to the shear) detected in Step S906 is xe2x88x922 in this alignment process performed in a major step. Therefore, as shown in FIG. 58, the setting of the stepper correction value at +3 in the next alignment in the same major step is expected to provide the overlay checking correction value which is zero. The calculated difference between the stepper correction value and the overlay checking correction value is referred to as a xe2x80x9ctrue shearxe2x80x9d which is expressed as
true shear=stepper correction valuexe2x88x92overlay checking correction valuexe2x80x83xe2x80x83(1)
The shorter a time difference between the present alignment and the next alignment, the smaller a change in the true shear. However, as the time difference increases, the true shear also increases. Then, the production control system body 6 controls a trend of the true shear in the same major step as shown in FIG. 59, and the alignment correction unit 6a calculates a mean value of true shears at P1 to P3 in the same major step as the stepper correction value to be set at tx in the next major step.
As above described, the conventional alignment correcting method corrects the stepper correction value for the wafer component to align a given pattern with its immediately below pattern, like the patterns 304 and 303.
An alignment correcting device for performing the above-mentioned alignment correcting method will be discussed below. FIG. 60 is a graph for illustrating an example of the conventional concept of the calculation for the stepper correction value for the wafer component. The graph of FIG. 60 shows the relationship between a data number and the true shear. Data with each data number of the graph are those for each group (lot). The time having elapsed since the alignment increases in ascending order of the numerical value of the data number i. In other words, the alignment with a higher data number is earlier than the alignment with a lower data number. A mean value of the data with data numbers 1 to 4 shown in FIG. 60 is simply calculated to provide a predicted stepper correction value. The predicted stepper correction value is calculated in accordance with the procedure shown in the flowchart of FIG. 61. The procedure of FIG. 61 is to perform the processing in Step S901 of FIG. 56. In Step 201, information of the past stored in the database 6b is searched for suitable data which are regarded as having been subjected to the stepper processing on the same conditions. Then, in Step 202, the stepper correction value for the wafer component is calculated on the assumption that the true shear equals the predicted stepper correction value. For instance, the calculation in Step S202 determines a mean value of true shears of the past to use the mean value as the stepper correction value for the wafer component. A term which calculates the mean value in an equation is referred to as an xe2x80x9caverage term.xe2x80x9d Likewise, the calculation in Step S203 determines a mean value of true shears of the past for each plane of the semiconductor device to use the mean value as the stepper correction value for the shot component for each plane.
FIG. 62 is a block diagram of a conventional alignment correcting device. An alignment data control unit 60 produces alignment data from a result of the overlay checking performed in the overlay checking device 5 to store the alignment data in the database 6b. The alignment correction unit 6a uses the alignment data stored in the database 6b to calculate the predicted stepper correction value. The alignment correction unit 6a outputs the calculated predicted stepper correction value to the stepper 4. The operation of portions of the alignment correction unit 6a for calculation of the predicted stepper correction value will be described below. An alignment data selection portion 61 selects data for use in calculation of the predicted stepper correction value, for example, by using tree information. The alignment data selection portion 61 outputs data associated with the wafer component among the selected data to a wafer component average term calculation portion 62, and outputs data associated with the shot component to a shot component average term calculation portion 65. The wafer component average term calculation portion 62 executes a calculation expressed by Equation (15) to be described later, that is, a calculation for determining a mean value of true shears for the predetermined number of groups (the predetermined number of lots). The wafer component average term calculation portion 62 outputs the calculation result as the predicted stepper correction value to the stepper 4. Likewise, the shot component average term calculation portion 65 executes the calculation expressed by Equation (15), that is, the calculation for determining a mean value of true shears for the predetermined number of lots. The shot component average term calculation portion 65 outputs the calculation result as the predicted stepper correction value to the stepper 4.
With the size reduction of semiconductor devices, the tolerance of the shear between patterns to be subjected to the alignment correction has become closer year after year. Under such situations, the constant satisfaction of design specifications for the tolerance of the shear between the patterns requires the increase in performance for the alignment correction as well as the increase in other performance of the semiconductor manufacturing device, and yet the increase in levels of function of the alignment correcting method. FIGS. 63 through 65 are graphs for illustrating the influences of abnormal data upon the shear between the patterns. For example, data about a plurality of lots processed by the same stepper 4 are shown in FIGS. 63 through 65, with respective data numbers corresponding to the processing sequence assigned thereto. The data about a lot with a data number i=2 are abnormal data resulting from, for example, erroneous measurement during the overlay checking. The abnormal data do not indicate a measurement value of a normal processing result but contain a value different from the measurement result due to misoperation and the like. The presence of the abnormal data with the data number i+2 causes an error in the stepper correction to generate consecutive out-of-specification data (with data numbers i and i+1) in subsequent processing. Specifically, since the true shear of the data with the data number i+2 shown in FIG. 63 is estimated to be greater than the actual true shear, a stepper set value for processing the lot associated with the data with the data number i+1 as shown in FIG. 64 is set at a high value. This causes the overlay checking result with the data number i+1 to be out of specifications (FIG. 65). Thus, the presence of the data with the data number i+2 makes the stepper correction value greater than necessary in the subsequent calculation of the predicted stepper correction value, resulting in a stronger likelihood that consecutive out-of-specification are generated.
In some cases, one of the factors which increase the likelihood of the out-of-specification data is that the overlay checking result immediately preceding the processing is not reflected in the calculation of the predicted stepper correction value. FIGS. 66A and 66B are a timing chart showing one situation of the conventional alignment correction. For instance, when the processing of a product B follows the processing of a product A, the processing of the product B at time t12 presents no problem. However, the product B is sometimes processed at time t11 before the completion of the overlay checking of the product A. In such a case, the overlay checking result of the product A which is the latest information is absent in the calculation of the predicted stepper correction value of the product B. For this reason, the alignment precision of the product B is not sufficiently ameliorated. If the product A provides out-of-specification data, the situation becomes worse, increasing the likelihood that the data about the subsequent product B are also out of specifications.
The background art alignment correcting method, semiconductor device manufacturing method, and alignment correcting device as above described have a drawback in that as the tolerance of the shear between patterns becomes closer, the alignment correction fails to bring the shear between the patterns within tolerance, making it difficult to satisfy the design specifications.
Further, abnormal data, if generated, are also subjected to the alignment correction to cause an error in the alignment correction. Then, the alignment correction increases the shear between patterns to make it difficult to satisfy the design specifications.
Moreover, alignment calibration which influences the calculation for the correction causes an error in the alignment correction to result in the shear between the patterns which is out of the tolerance of the design specifications.
Furthermore, the increases in complexity of semiconductor device structures and in variety of product types developed on the market cause the increases in type and amount of data required for alignment control. Accordingly, the storage of data for alignment control requires excessive handling.
A first aspect of the present invention is intended for a method of correcting alignment using true shears for a plurality of groups of products regarded as being subjected to stepper processing on the same condition. According to the present invention, the method comprises the steps of: calculating a mean value of the true shears for the plurality of groups of products; calculating a difference in true shear between at least two groups of products which are manufactured consecutively among the plurality of groups of products; and adding a value proportional to the difference in true shear to the mean value to calculate a predicted stepper correction value.
Preferably, according to a second aspect of the present invention, in the method of the first aspect, the step of calculating the stepper correction value uses a proportionality constant which minimizes a variation in true shear to calculate the value proportional to the difference in true shear.
Preferably, according to a third aspect of the present invention, in the method of the second aspect, the step of calculating the stepper correction value comprises the step of detecting the proportionality constant in a range from xe2x88x921 to 1.
Preferably, according to a fourth aspect of the present invention, in the method of the first aspect, the step of calculating the mean value comprises the step of determining a mean value of true shears for not less than three groups of products.
A fifth aspect of the present invention is intended for a method of correcting alignment using true shears for a plurality of groups of products regarded as being subjected to stepper processing on the same condition. According to the present invention, the method comprises the steps of: detecting whether or not the true shears fall within a predetermined range; and calculating a predicted stepper correction value without using a true shear which is outside the predetermined range.
A sixth aspect of the present invention is intended for a method of correcting alignment using true shears for a plurality of groups of products regarded as being subjected to stepper processing on the same condition. According to the present invention, the method comprises the steps of: extracting a group of products processed immediately previous to a product for which a predicted stepper correction value is to be calculated; judging whether or not a measurement has been made on true shears for the group of products; and providing an instruction for inhibiting exposure using calculation of the predicted stepper correction value when the measurement has not yet been made.
According to a seventh aspect of the present invention, a method of correcting alignment comprises the steps of: judging whether or not stepper processing is performed on products of the same type; extracting a true shear for a product of the same type which is processed immediately previously; and determining a predicted stepper correction value, the predicted stepper correction value being the extracted true shear when the true shear is extracted in the extracting step, the predicted stepper correction value being a predetermined value when the true shear is not extracted in the extracting step.
According to an eight aspect of the present invention, a method of manufacturing a semiconductor device comprises the step of positioning patterns using a method of correcting alignment as recited in any one of the first to seventh aspects.
A ninth aspect of the present invention is intended for a device for correcting alignment using true shears for a plurality of groups of products regarded as being subjected to stepper processing on the same condition. According to the present invention, the device comprises: an average term calculation portion for calculating a mean value of the true shears for the plurality of groups of products; a variable term calculation portion for calculating a difference in true shear between at least two groups of products which are manufactured consecutively among the plurality of groups of products; and an addition portion for adding a value proportional to the difference in true shear to the mean value to calculate a predicted stepper correction value.
A tenth aspect of the present invention is intended for a semiconductor device manufactured using a method of correcting alignment as recited in any one of the first to seventh aspects or a device for correcting alignment as recited in the ninth aspect.
As described hereinabove, the method of correcting alignment in accordance with the first aspect of the present invention, wherein the value proportional to the true shear difference between the at least two groups of products manufactured consecutively is reflected in the predicted stepper correction value, increases an alignment correction precision.
In the method of correcting alignment in accordance with the second aspect of the present invention, the proportionality constant may be conditioned to greatly increase the alignment correction precision.
In the method of correcting alignment in accordance with the third aspect of the present invention, the limitation of the range within which the proportionality constant is detected eliminates the handling of calculation.
In the method of correcting alignment in accordance with the fourth aspect of the present invention, the number of groups for which the mean value is calculated is conditioned to greatly increase the alignment correction precision.
In the method of correcting alignment in accordance with the fifth aspect of the present invention, the elimination of abnormal data increases the alignment correction precision.
The method of correcting alignment in accordance with the sixth aspect of the present invention, wherein the immediately preceding true shear is constantly reflected in the calculation of the predicted stepper correction value, increases the alignment correction precision.
The method of correcting alignment in accordance with the seventh aspect of the present invention directly uses the true shear for the product of the same type, thereby reducing the number of data to be stored.
The method of manufacturing the semiconductor device in accordance with the eighth aspect of the present invention or the semiconductor device in accordance with the tenth aspect thereof may increase a pattern positioning precision with the increase in the alignment correction precision.
The device for correcting alignment in accordance with the ninth aspect of the present invention, wherein the value proportional to the true shear difference between the at least two groups of products manufactured consecutively is reflected in the predicted stepper correction value, increases the alignment correction precision.
It is therefore an object of the present invention to improve an alignment precision over a conventional alignment precision in an alignment correcting method, a semiconductor device manufacturing method, and an alignment correcting device.
It is another object of the present invention to eliminate the influence of abnormal data, if generated, upon alignment correction to prevent a shear between patterns from increasing due to the abnormal data and being out of tolerance.
It is still another object of the present invention to simplify the storage of alignment conditions to reduce the time required to store data in an alignment correcting method, a semiconductor device manufacturing method, and an alignment correcting device.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.